function(input, output, session) {
  # 格式化输出，插入对话者身份前缀。
  formatOutput<-function(messages){
    outStr<-""
    for(i in 2: length(messages)){
      message = messages[[i]]
      # print(message)
      if (i%%2==0){
        outStr<-paste(outStr,"User: ",message[["content"]],"\n",sep="")
      }else{
        if(is.null(message[["content"]]))
          outStr<-paste(outStr,"AI: ",message[["function_call"]],"\n\n",sep="")
        else
          outStr<-paste(outStr,"AI: ",message[["content"]],"\n\n",sep="")
      }
    }
    return (outStr)
  }
  
  ifContext<- reactive({
    input$ifContext
  })
  
  ifFunctionCall<- reactive({
    input$ifFunctionCall
  })
  
  prompt<- reactive({
    input$prompt
  })
  
  observeEvent(input$clearContext,{
    session$userData$context<- context
    updateTextAreaInput(session, "context", value = "")
  })

  observeEvent(input$clearLast,{
    context<-session$userData$context
    context<-context[1:length(context)-1]
    outStr<- formatOutput(context)
    session$userData$context<-context
    updateTextAreaInput(session, "context", value = outStr)
  })  
  
  observeEvent(input$sendout,{
    if(ifContext() && ! is.null(session$userData$context)){
      temp<-session$userData$context
    } else{
      temp<- context
    }
    
    temp[[length(temp)+1]]<-list(role="user",content=prompt())
    # Show notification while querying.
    id <- showNotification("正在询问ChatGPT...", duration = NULL, closeButton = FALSE)
    on.exit(removeNotification(id), add = TRUE)
    
    # Catch exceptions happened while calling OpenAI API
    errmessage = NULL
    tryCatch({
      temp<-conversation(temp, ifFunctionCall())
    },error = function(err) {
      # print(err)
      # Use <<- to pass error message outside
      errmessage<<-list(role="assistant",content=paste("ERROR:  ",err))
    })
    if (!is.null(errmessage))
      temp[[length(temp)+1]]<-errmessage
    
    session$userData$context<- temp
    outStr<-formatOutput(temp)
    updateTextAreaInput(session, "context", value = outStr)
    updateTextAreaInput(session, "prompt", value = "")
  })
  
}